In accordance with recent developments in techniques, compact, light personal computers (hereinafter also referred to as "portable computers" or "notebook computers") are being designed and manufactured for which portability is an important consideration, and such computers are in wide, practical use.
In FIG. 11 is shown a common notebook computer. The notebook computer comprises a thin main body and a display unit that is rotatably coupled to the main body.
The main body includes a shallow case. A keyboard unit, that serves as an input device, is provided on the top surface of the case. In the case are retained a system board, on which are mounted a CPU, RAM, ROM and a variety of peripheral controllers; auxiliary storage devices, such as a hard disk drive and a CD-ROM; and a battery/power supply circuit (not shown). The keyboard unit also serves as the upper face of the case and also shields the interior of the main body.
The display unit is constituted by a shallow rear cover, and a front bezel that supports a liquid crystal display panel that is positioned almost in the center of the cover. Inside the display unit that is enclosed by the front bezel and the rear cover, a backlight unit is provided for illuminating the images produced on the liquid crystal display panel. The backlight unit includes a backlight (cold-cathode tube: CFL), a light conducting plate, and a light diffusion plate (none of which are shown in FIG. 11). A pair of almost cylindrical protrusions are integrally formed at the lower edge of the display unit. These protrusions engage and are hinged at bearings on the main body so that they rotatably support the display unit.
As a consequence of the fact that a notebook computer can be used in a mobile environment, i.e., while being carried or an arbitrary location outside the office, and that a user's needs may vary, employment applications for the notebook computers also vary accordingly. The employment of a notebook computer as auxiliary presentation means is a typical example. For this application, members (a rear cover and a light diffusion plate) on the rear face of the liquid crystal display panel are removed to make the panel transparent, and the notebook computer is then placed atop the light source for an overhead projector (OHP) for use as a file. A notebook computer designed for a presentation needs is disclosed in, for example, Japanese Patent Application No. Hei 7-43851 and Hei 7-43925, both of which are assigned to the present assignee. Notebook computer "IBM ThinkPad 755CV/CDV," which is sold by IBM Japan, Co., Ltd., can be mounted on an OHP. Another application example for a notebook computer is as a pen input computer that is used by positioning, on a display panel, a plate (tablet) for which pressure or electromagnetic induction is used to detect designated coordinates.
One measure that is taken to improve such OHP use and the usability of pen input is the provision of a liquid crystal display panel so designed that it can be detached from a main body, the liquid crystal display panel and the main body being connected by a cable (see FIG. 12). In this case, exchange of input/output signals for the liquid crystal display panel and an input tablet and a power supply are performed via the cable. Once the liquid crystal display panel has been removed from the body, it has no mechanical contact nor force by the main body other than the cable. Thus, a user can freely employ the display panel within a range allowed by the length of the cable. For OHP use, it is easier to position the liquid crystal display panel on an OHP light source once it has been removed from the notebook computer. For pen input, the input operation can be performed more stably with a tablet removed from the main body and placed on a desk than with a tablet that is hinged with the main body.
A portable computer whereof a liquid crystal display panel is detachable from the main body and whereof the main body and the liquid crystal display panel are connected by a cable is disclosed in, for example, Japanese Unexamined Patent Publication Nos. Hei 2-210524, Hei 2-228690, Hei 3-1184.
As is mentioned in the previous sub-division, a structure wherein a liquid crystal display panel is detachable from the main body of a portable computer is very useful when the portable computer is used for operations other than for ordinary keyboard input (i.e., for use with an OHP and for pen input). It is obvious that usability will be enhanced if the detachment of the display panel can be performed even while the main body is powered on, i.e., is being operated. While inputting data or editing text at the keyboard of a notebook computer, a user can give a presentation or can change to pen input without the complete closing of a currently executing program being required, merely by removing a liquid crystal display panel and connecting it to the main body of a computer with a cable.
The liquid crystal display panel and the main body are electrically connected to each other. In the power-ON state, i.e., during the exchange of electric signals between the two sections, a disorderly electric disconnection or a reboot may result in some problems, such as the deterioration of the hardware. These problems will now be briefly explained.
(1) A liquid crystal display panel is powered by the main body, and driven by the RGB video signals and a sync signal from a video controller that is incorporated in the main body. In other words, the liquid crystal display panel is an output device and outputs no signals to the main body. A power ON/OFF sequence for the liquid crystal display panel, and input timing for video and sync signals, strictly conform to the standardized specification of this art. When the liquid crystal display panel is detached during the system operation, this may be a violation of the standards, and when, for example, signal output lines and a power line are opened at a disorderly timing, deterioration of hardware may occur.
(2) When a liquid crystal display panel serves as an input tablet, an output signal is sent from the tablet to the main body. Normally, the system monitors this tablet output signal as a peripheral device input. When the input line is disorderlily disconnected, an erroneous input will occur at the main body occurs and will cause the computer to hang up.
That is, careless detachment of the liquid crystal display panel from the computer main body during system operation will cause the system to malfunction and the hardware to deteriorate.
In addition, several tens of seconds to several minutes are normally required to remove the liquid crystal display panel/input tablet from the main body and to connect it to the main body by cable. During such removal/attachment process, a currently active application may be progressed, so that a user may not be able to recover the contents of the progressed application when the re-connection is completed. For a user it is very inconvenient to completely close down a currently active program (an OS or an application) and turn off the power each time the liquid crystal display panel/input tablet is disconnected, and to turn on the power and restart the program when the display panel and the main body are reconnected.
However, Japanese Unexamined Patent Publication No. Hei 210524, Hei 2-228690 and Hei 3-1184 disclose only that the liquid crystal display panel is mechanically detachable, and do not teach the hardware related electric problem associated with the detachment process during the system operation, and the problem that arises as a result of the loss of the contents of an application, i.e., on the interruption of a task.
It is therefore one object of the present invention to provide a superior portable information processing apparatus that comprises a main body, in which a primary controller and media are retained; and a display unit, which is rotatively hinged at the rear edge of the main body and which has an internally mounted liquid crystal display panel/input tablet.
It is another object of the present invention to provide a superior portable information processing apparatus having a liquid crystal display panel/input tablet that is detachable from a main body.
It is an additional object of the present invention to provide a superior portable information processing apparatus having a liquid crystal display panel/input tablet that can be detached from the apparatus even when the main body is powered on, i.e., is being operated.
It is a further object of the present invention to provide a superior portable information processing apparatus wherewith, even though a liquid crystal display panel is detached from/attached to the apparatus while a program is being executed by the main body, a user does not lose the contents of the program that has being executed during the detachment/attachment process.